The invention discloses a spontaneous polarization field enhanced ultraviolet detector based on BeZnOS quaternary alloy and a preparation method thereof. The detector includes, in order from bottom totop, an m-plane sapphire substrate, an active layer and a pair of parallel metal electrodes, the active layer is an m-plane BeZnOS quaternary alloy film, and the parallel metal electrodes are perpendicular to the c-axis direction of the BeZnOS quaternary alloy film. An epitaxial m-plane BeZnOS film is grown on the single crystal m-plane sapphire, a metal electrode perpendicular to the c-axis of the film is evaporated, a spontaneous polarization electric field and an external electric field are fully utilized and stacked to enhance and promote the separation of a photon-generated carrier so asto enhance the light detection capacity. Besides, the ultraviolet light detector of the MSM structure is simple, the manufacturing process is simple, the detector has a good detection capacity for the ultraviolet light with the 300 nm wavelength, the response speed is fast, the dark current is small, and the performances are stable.